LT8580 datasheet(13/32 Pages) LINER

13 / 32 page

LT8580

8580fa

For more information www.linear.com/LT8580

applicaTions inForMaTion

As with any feedback loop, identifying the gain and phase

contribution of the various elements in the loop is critical.

Figure5showsthekeyequivalentelementsofaboostcon-

verter. Because of the fast current control loop, the power

stage of the IC, inductor and diode have been replaced by

a combination of the equivalent transconductance ampli-

fier gmp and the current controlled current source which

converts IVIN to (hVIN/VOUT) • IVIN. gmp acts as a current

source where the peak input current, IVIN, is proportional

to the VC voltage. h is the efficiency of the switching

regulator, and is typically about 85%.

Note that the maximum output currents of gmpandgmaare

finite.ThelimitsforgmpareintheElectricalCharacteristics

section (switch current limit), and gmaisnominallylimited

to about +15µA and –17µA.

Figure 5. Boost Converter Equivalent Model

–

gma

CC: COMPENSATION CAPACITOR

COUT: OUTPUT CAPACITOR

CPL: PHASE LEAD CAPACITOR

CF: HIGH FREQUENCY FILTER CAPACITOR

gma: TRANSCONDUCTANCE AMPLIFIER INSIDE IC

gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER

RC: COMPENSATION RESISTOR

RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD(MAX)

RO: OUTPUT RESISTANCE OF gma

R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK

RESR: OUTPUT CAPACITOR ESR

η: CONVERTER EFFICIENCY (~85% AT HIGHER CURRENTS)

8580 F05

FBX

COUT

CPL

RESR

VOUT

IVIN

gmp

1.204V

REFERENCE

η • VIN

VOUT

•IVIN

From Figure 5, the DC gain, poles and zeros can be cal-

culated as follows:

Output Pole: P1=

2 • π • RL • COUT

Error AmpPole: P2 =

2 • π • RO +RC

[

] • CC

Error Amp Zero: Z1=

2 • π • RC• CC

DC Gain:

(Breaking Loop at FBX Pin)

ADC = AOL(0) =

∂VC

∂VFBX

• ∂IVIN

∂VC

•

∂VOUT

∂IVIN

• ∂VFBX

∂VOUT

gma • R0

(

)• gmp• h •

VIN

VOUT

• RL

⎛

⎝

⎜

⎞

⎠

⎟ •

0.5R2

R1+ 0.5R2

ESR Zero: Z2 =

2 • π • RESR • COUT

RHP Zero: Z3 =

VIN2 • RL

4 • π • VOUT

• L

HighFrequency Pole: P3 >

Phase Lead Zero: Z4 =

2 • π • R1• CPL

Phase LeadPole: P4 =

2 • π •

R1• R2

R1+ R2

• CPL

Error Amp Filter Pole:

P5 =

2 • π • RC • RO

RC +RO

• CF

,CF <

The current mode zero (Z3) is a right-half plane zero

which can be an issue in feedback control design, but is

manageable with proper external component selection.

LT8580 датащи(PDF) 13 Page - Linear Technology

LT8580 датащи(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

датащи скачать

ссылки URL